A phase II study of dual immune checkpoint blockade (ICB) plus androgen receptor (AR) blockade to enhance thymic T-cell production and immunotherapy response in metastatic breast cancer (MBC).

Abstract

TPS1106 Background: ICB (atezolizumab, anti-PD-L1) is known to improve survival when added to chemo, however only in PD-L1-positive, triple-negative MBC. ICB is less effective in hormone receptor positive (HR+) MBC, or when administered following palliative chemo. Novel approaches are required to broaden clinical benefit of ICB, particularly in PD-L1-negative, HR+, or chemo-experienced MBC. Dual ICB with anti-PD-1 (nivolumab) and anti-CTLA-4 (ipilimumab) is associated with enhanced activity in melanoma other malignancies, but has not been explored extensively in MBC. Androgen receptor (AR) blockade, in addition to known direct cytostatic effects in AR-expressing MBCs (50% of TNBC, > 75% of HR+ MBC), may also modulate immune response. AR blockade has been shown experimentally to stimulate thymic production of naïve T-cell clones, which in turn can facilitate de novo anti-tumor immune responses. Concurrent ICB can enhance the activity of these T-cell clones by interfering with PD-1-mediated peripheral tolerance. This combination approach is promising in MBC in light of known AR positivity, and the routine use of lymphodepleting chemo regimens in the curative-intent setting. Methods: This is a phase II trial of dual immune checkpoint blockade (nivolumab 240mg IV q2w; ipilimumab 1mg/kg IV q6w) plus AR blockade (bicalutamide, 150mg PO daily, dose reduction allowed) in triple-negative MBC (cohort A: AR-positive [ > 1% by IHC]; cohort B: AR-negative) or HR+ MBC (cohort C) in subjects who received 0/1 prior chemotherapies in the non-curative setting. Objectives include 24-week clinical benefit rate by iRECIST (primary), safety (CTCAE v4.0), and other response measures (RECIST1.1, PFS, OS). Efficacy for each cohort is defined as > 20% improvement in response over historical control (30% per EMBRACE clinical trial) employing a Simon 2-stage design to minimize futility (n = 46/cohort, stage I n = 15). Thymic generation of T-cells will be measured via quantitative deep sequencing of T-cell receptors (TcR, ImmunoSEQ assay) and TcR excision circles (TRECs), as well as real-time flow cytometry using surrogate cell surface markers of recent thymic emigration. Enrollment has commenced, sites: Earle A. Chiles Research Institute (Portland, OR), Memorial Sloan Kettering Cancer Center (New York, NY). Clinical trial information: NCT03650894.